Instrument for intra-operative implant templating using fluoroscopy

ABSTRACT

A surgical instrument having a first assembly with a first radio-opaque portion providing a profile of a first portion of an intramedullary implant or canal in a bone, and a second assembly having a second radio-opaque portion providing a profile of a second portion of the intramedullary implant or canal. The surgical instrument may also include a third radio-opaque portion providing an alignment feature to provide a fluoroscopic planar check for the surgical instrument.

This application is a continuation of U.S. patent application Ser. No.14/096,831, filed on Dec. 4, 2013, which is a non-provisional of U.S.Patent Application No. 61/736,323, which was filed Dec. 12, 2012, theentireties of which are incorporated by reference herein.

FIELD OF DISCLOSURE

The disclosed system and method generally relate to surgical guides andinstruments. More specifically, the disclosed system and method relateto surgical guides and instruments for orthopedic procedures.

BACKGROUND

Total joint replacement prostheses typically include a speciallydesigned jig or fixture to enable a surgeon to make accurate and precisebone resections in and around the joint being prepared to accept theprosthesis. The ultimate goal with any total joint prosthesis is toapproximate the function and structure of the natural, healthystructures that the prosthesis is replacing. Should the prosthesis notbe properly attached to the joint or not properly aligned, discomfort tothe patient, gait problems, or degradation of the prosthesis may result.

Many surgical procedures employ the use of intra-operative fluoroscopyto check the alignment of the intramedullary cavities that are preparedto receive the joint replacement prosthesis; however, the use ofintra-operative fluoroscopy may have drawbacks. One such drawback isthat the use of fluoroscopy to check the alignment of intramedullarycavities formed during surgery may increase the overall length of thesurgical procedure as time is taken to acquire and evaluate thefluoroscopic images. Long surgery times may lead to increased tourniquettime for the patient and may therefore increase recovery time.

Another drawback of fluoroscopy is exposing the patient and others inthe operating room to the ionized radiation. For example, the U.S. Foodand Drug Administration (“FDA”) has issued several articles and publichealth advisories concerning the use of the fluoroscopy during surgicalprocedures. Consequently, even though steps are taken to protect thepatient and other from the ionized radiation, it is virtually impossibleto eliminate all risk associated with the ionized radiation.

Thus, it is desirable to overcome the limitations of the prior art andprovide an efficient fluoroscopic check of the implant or prosthesesand/or of the intramedullary cavities with or without the assistance ofa preoperative plan or assessment.

SUMMARY

One embodiment of the present subject matter provides a surgicalinstrument having a first assembly with a first radio-opaque portionproviding a profile of a first portion of an intramedullary implant orcanal in a bone, and a second assembly with a second radio-opaqueportion providing a profile of a second portion of the intramedullaryimplant or canal. These portions of the intramedullary implant mayrepresent the stem of a prospective implant.

Another embodiment of the present subject matter provides a surgicalinstrument having a first module with a first radio-opaque portionproviding a profile for an intramedullary implant or canal in a bone,and a second module with a second radio-opaque portion providing aprofile for the intramedullary implant or canal in the bone. These firstand second modules may provide an alignment check for the implant in twodifferent planes. Further, any one or both of the first and secondmodules may include a first assembly having a third radio-opaque portionproviding a profile of a first portion of an intramedullary implant orcanal in a bone, and a second assembly having fourth and fifthradio-opaque portions, the fourth radio-opaque portion providing analignment feature for the surgical instrument and the fifth radio-opaqueportion providing a profile of a second portion of the intramedullaryimplant or canal whereby the third, fourth and fifth radio-opaqueportions are subsets of the respective first and second radio-opaqueportions.

An additional embodiment of the present subject matter provides asurgical instrument including a first assembly with a first radio-opaqueportion providing a profile of a first portion of an intramedullaryimplant or canal in a bone, and a second assembly with a secondradio-opaque portion providing an alignment feature for the surgicalinstrument.

These embodiments and many other objects and advantages thereof will bereadily apparent to one skilled in the art to which the inventionpertains from a perusal of the claims, the appended drawings, and thefollowing detailed description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the bones of a human foot and ankle.

FIG. 2 is a perspective view of a surgical instrument according to oneembodiment of the present subject matter.

FIG. 3 is a front plan view of a surgical instrument according toanother embodiment of the present subject matter.

FIG. 4 is a fluoroscopic view of a surgical instrument according to oneembodiment of the present subject matter in a non-aligned position.

DETAILED DESCRIPTION

With reference to the figures, where like elements have been given likenumerical designations to facilitate an understanding of the presentsubject matter, the various embodiments of an instrument forintra-operative implant templating using fluoroscopy are described.

It should be noted that the figures are not necessarily to scale andcertain features may be shown exaggerated in scale or in somewhatschematic form in the interest of clarity and conciseness. In thedescription, relative terms such as “horizontal,” “vertical,” “up,”“down,” “top” and “bottom” as well as derivatives thereof (e.g.,“horizontally,” “downwardly,” “upwardly,” etc.) should be construed torefer to the orientation as then described or as shown in the drawingfigure under discussion. These relative terms are for convenience ofdescription and normally are not intended to require a particularorientation. Terms including “inwardly” versus “outwardly,”“longitudinal” versus “lateral” and the like are to be interpretedrelative to one another or relative to an axis of elongation, or an axisor center of rotation, as appropriate. Terms concerning attachments,coupling and the like, such as “connected” and “interconnected,” referto a relationship wherein structures are secured or attached to oneanother either directly or indirectly through intervening structures, aswell as both movable or rigid attachments or relationships, unlessexpressly described otherwise. When only a single machine isillustrated, the term “machine” shall also be taken to include anycollection of machines that individually or jointly execute a set (ormultiple sets) of instructions to perform any one or more of themethodologies discussed herein. The term “operatively connected” is suchan attachment, coupling or connection that allows the pertinentstructures to operate as intended by virtue of that relationship. In theclaims, means-plus-function clauses, if used, are intended to cover thestructures described, suggested, or rendered obvious by the writtendescription or drawings for performing the recited function, includingnot only structural equivalents but also equivalent structures.

The disclosed systems and methods may advantageously utilize custommanufactured surgical instruments, guides, and/or fixtures that arebased upon a patient's anatomy to reduce the use of fluoroscopy during asurgical procedure. These custom instruments, guides, and/or fixturesmay be created by imaging a patient's anatomy with a computer tomography(“CT”) scanner, a magnetic resonance imaging (“MRI”) machine, or likemedical imaging technology prior to surgery and utilizing these imagesto create patient-specific instruments, guides, and/or fixtures. This isgenerally termed as a preoperative assessment or plan and may be used inconjunction with intra-operative tools to accurately implement such aplan. Exemplary preoperative assessments or plans may allow a surgeon tospecify the size, position and orientation of a patient's anatomicalcomponents and/or subsequent implant components within the joint or boneat issue based upon preoperative CT or MRI images. Of course, finalcomponent size and position may be determined intra-operatively throughdirect visualization by the surgeon with or without the aid offluoroscopy.

Although the following description of the custom patient-specificinstruments are described with respect to a foot 10 and ankle 12, oneskilled in the art will understand that the systems and methodsdescribed herein may be utilized in connection with other joints andrespective bones including, but not limited to, knees, hips, arms,shoulders, and the like. Thus, the claims appended herewith should notbe so limited to an ankle and the bones associated therewith. As shownin FIG. 1, a typical human foot 10 includes an ankle joint 12 formedbetween a talus 14, which is disposed on a calcaneus 20, and a tibia 16and fibula 18.

A CT or MRI scanned image or series of images may be taken of apatient's ankle 12 (or other joint and respective bones) and thenconverted from, e.g., a DICOM image format, to a solid computer model ofthe ankle including the calcaneus, talus, tibia, navicular, and fibulato determine implant alignment, type, and sizing using specializedmodeling methods that are often embodied in computer software. Computergenerated solid models that are derived from the data of the CT or MRIscan image will often include precise and accurate information regardingthe surface contours surrounding the structures that have been imaged,e.g., the surface topography of the bones or contour of fascia that havebeen imaged. It will be understood that by surface topography it ismeant the location, shape, size and distribution of surface featuressuch as concavities and prominences or the like. The methods disclosedin U.S. Pat. No. 5,768,134, issued to Swaelens et al., which isincorporated by reference herein in its entirety, have been found toyield adequate conversions of data of CT or MRI scan images to solidcomputer models. In some embodiments, images are made of a foot 10,i.e., the calcaneus 20, talus 14, tibia 16, and fibula 18 of a patientusing a CT or MRI machine, or other digital image capturing andprocessing unit as is understood by one skilled in the art and a modelgenerated.

FIG. 2 is a perspective view of a surgical instrument according to oneembodiment of the present subject matter. With reference to FIG. 2, asurgical instrument 30 according to one embodiment of the presentsubject matter may be used in conjunction with patient-specificalignment guides to act as an intraoperative implant template. With sucha template instrument attached to a patient-specific alignment guide andwith the patient-specific alignment guide attached to the patient'sanatomy, an exemplary instrument may be used to evaluate a prospectiveor resulting implant or prosthesis size, placement and orientation priorto committing to the location of the patient-specific alignment.Exemplary instruments according to embodiments of the present subjectmatter may be used in conjunction with a preoperative assessment of planwhich may represent the planned location of a patient specific guidewith fluoroscopic check features over the patient's CT or MRI scanderived anatomy for side-by-side comparison against intraoperativeimaging. As illustrated, the surgical instrument 30 may include a firstassembly 35 having both radiolucent 37 and radio-opaque portions 36, 38.These radio-opaque portions may be comprise of a metal or otherradio-opaque material. These radio-opaque portions 36, 38 may alsoprovide an alignment indication 36 of the assembly 35 and/or may providea profile 38 of a first portion of a prospective or resultingintramedullary implant or canal for a bone (not shown). Exemplary bonesmay be, but are not limited to, the tibia, femur, humerus, radius, ulna,vertebrae, and fibula. Further, the provided alignment indication 36 mayrepresent the position or alignment of a portion of the implant with alongitudinal axis of the bone, the position of a portion of the implantwith a transverse axis of the bone, the position of a portion of theimplant with a resection plane of the bone, a drill location for thebone, a drill orientation for the bone, and/or the position of a portionof the implant with an axis of the implant stem.

The surgical instrument 30 may also include a second assembly 40 havinga second radio-opaque portion 30 which provides a profile 42 of a secondportion of the prospective or resulting intramedullary implant or canal.In one embodiment, the first and/or second portions of theintramedullary implant may be the stem of the implant or may be thesilhouette of the intramedullary canal accepting an implant. The secondassembly 40 may also include a third radio-opaque portion 43, 44 whichprovides an alignment feature for the surgical instrument 30.Embodiments of the present subject matter may thus allow forintraoperative checks (e.g., fluoroscopic) in multiple planes to ensureproper positioning of implants, intramedullary canals, drill locationsand the like. For example, one exemplary alignment feature may be a pegor rod 43 and a ring or cylinder 44 whereby the ring 44 substantiallycircumscribes the peg 43 upon planar alignment, e.g., Anterior-Posterior(A-P) alignment, of the instrument 30. Of course, such an alignmentfeature is exemplary only and the claims appended herewith should not beso limited as a myriad of alignment features using Kirschner wires,fiducial markers and other radio-opaque features may be employed byembodiments of the present subject matter. A further embodiment of thepresent subject matter may include a first assembly 35 having a firstradio-opaque portion(s) 38 providing a profile of a first portion of anintramedullary implant in a bone and a second assembly 40 having onlythe radio-opaque portion 43, 44 which provides the planar alignmentfeature for the surgical instrument 30.

In another embodiment, the second assembly 40 may include a hole 46 orother attachment mechanism adaptable to attach an extra-medullaryalignment rod (not shown) to the instrument 30. The surgical instrument30 may include one or more lateral segments 45 that are adaptable toattach additional first assemblies and/or second assemblies thereto(see, e.g., FIG. 3). These additional first and second assemblies maythus provide a profile of the intramedullary implant or canal in adifferent and/or orthogonal plane (e.g., coronal, sagittal plane). Pegs,rods 47 or another attachment mechanism may be provided on or in thesurgical instrument 30 for attaching a resection guide, drill guidesand/or drill orientation guides thereto.

FIG. 3 is a front plan view of a surgical instrument according toanother embodiment of the present subject matter. With reference to FIG.3, a surgical instrument 50 according to another embodiment of thepresent subject matter is illustrated attached to a tibia 16 and mayinclude a first module 55 having a radio-opaque portion 57 providing aprofile for a prospective or resulting intramedullary implant or canalfor the tibia 16 (or other bone) and/or alignment features. The surgicalinstrument 50 may also include a second module 60 having a radio-opaqueportion 62 providing a profile for the prospective or resultingintramedullary implant or canal in the bone and/or alignment features.As illustrated in FIG. 3, the first and second modules 55, 60 mayprovide an alignment check for the intramedullary implant or canal intwo different planes (e.g., orthogonal, sagittal, coronal, etc.). Withreference to FIG. 2, any one or both of the first and second modules 55,60 illustrated in FIG. 3 may include first assemblies 35 having bothradiolucent and radio-opaque portions whereby the radio-opaque portionsmay provide planar, linear or other alignment indications and/or mayprovide a profile of a first portion of an intramedullary implant orcanal in the tibia 16. Of course, while a tibia 16 has been illustratedin FIG. 3, the claims appended herewith should not be so limited as itis envisioned embodiments of the present subject matter may provide aprofile and/or alignment features for a prospective or resultingintramedullary implant or canal in the femur, humerus, radius, ulna,vertebrae, fibula, etc. Additionally, any one or both of the first andsecond modules 55, 60 may also include second assemblies 40 havingradio-opaque portions which may provide a profile of a second portion ofthe intramedullary implant or canal and/or may provide an alignmentfeature for the surgical instrument 50. While an exemplary alignmentfeature may be a peg and a ring whereby the ring substantiallycircumscribes the peg upon planar alignment of the instrument 50, theappended claims herewith should not be so limited. As illustrated in thesecond module 60 of FIG. 3, the exemplary alignment feature consistingof a peg and ring may be laterally or longitudinally offset from eachother to provide an adequate planar fluoroscopic alignment view orindication. Again, such an alignment feature is exemplary only and theclaims appended herewith should not be so limited as a myriad ofalignment features using Kirschner wires, fiducial markers and otherradio-opaque features may be employed by embodiments of the presentsubject matter. Further, any one or both of the modules 55, 60 may alsoinclude resection guides, drill guides, drill orientation guides. Whilenot shown, additional modules may also be included on an exemplaryinstrument 50 via the lateral segments to provide additional alignmentand/or profile features in other planes.

FIG. 4 is a fluoroscopic view of a surgical instrument according to oneembodiment of the present subject matter in a non-aligned position. Withreference to FIG. 4, an exemplary surgical instrument 70 is shownillustrating misalignment of an intramedullary canal 72 through the lackof alignment of the radio opaque portions 82 of the first assembly 80and the radio opaque portions 92 of the second assembly 90 during anintraoperative fluoroscopic check. Further, the surgical instrument 70is shown in a non-aligned planar view as the ring or cylinder 44 doesnot substantially circumscribe the respective peg 43.

Embodiments of the present subject matter illustrated in FIGS. 2-4 anddescribed above may be used to assist in obtaining a true view in theintended direction via a gun-sight (e.g., circumscribed peg, fiducialmarkers, Kirschner wires, etc.) or alignment indication and may alsoprovide an outline, silhouette, or overlay of one or more implants orintramedullary features. Such embodiments may allow for the attachmentof other instruments that may assist in the physical alignment, sizing,pin placement, etc. of surgical guides and instruments (e.g.,extra-medullary rod, drop rod, resection guides, drill guides, and thelike). These exemplary embodiments may be used to ensure that animplant, such as a tibial implant may be properly inserted, aligned, andimplanted into a respective tibia by conventional means including theremoval of bone material from the tibia, fibula and/or talus usingchisels, screws, drills, reamers and other conventional removal tools.The tibia, fibula and/or talus may then be sized, reshaped and/orresected to accept appropriate talar, tibial and/or fibular fixtures orimplants. These fixtures may be mechanically affixed to the respectivebone by screws, nails, bone cement and the like and may havesurface-matched shapes specific to a patient's anatomy. One exemplaryimplant may be, but is not limited to, a Wright Medical Technologies,Inc. INBONE® total ankle system. The tibial implant may include alaterally extending tray or base shaped to conform to the patient'sdistal tibia after the distal portion of the tibia has beenappropriately shaped and resected. The tibial implant or prosthesis mayalso include a stem or plug, sectioned or otherwise, extending generallyperpendicular to a plane formed by the tibial base. The stem may beplaced in a surgically formed opening extending into a patient'sintramedullary canal. A plastic, polymeric insert may also be attachedto the tibial base which provides a tibial articulating surface thatarticulates with the movement of the respective joint. A non-limiting,exemplary system and method for an ankle replacement is described inco-pending U.S. application Ser. No. 13/330,091 filed Dec. 19, 2011 andU.S. application Ser. No. 12/711,307, filed Feb. 24, 2010, the entiretyof each being incorporated herein by reference.

Although reference has been made to a patient's talus, tibia, fibula,and ankle joint, one skilled in the art will understand that embodimentsof the present subject matter may be implemented for other joints andrespective bones including, but not limited to, the knee, hip, shoulder,or other joints. Thus, the disclosed devices and methods mayadvantageously utilize custom manufactured surgical instruments, guides,and/or fixtures that are based upon a patient's anatomy to reduce theuse of fluoroscopy during a surgical procedure for a multitude of jointsand respective bones.

One aspect of embodiments of the present subject matter is to provide amodular instrument to be used in conjunction with patent-specificalignment guides to act as an intraoperative implant template. With sucha template instrument attached to a patient-specific alignment guide andwith the patient-specific alignment guide attached to the patient'sanatomy, an exemplary instrument can be used to evaluate the prospectiveor resulting implant size, placement and orientation prior to committingto the location of the patient-specific alignment.

A further aspect of embodiments of the present subject matter may assistin obtaining a true view in the intended direction of implantation viavarious alignment features and may also provide the outline, silhouette,or overlay of one or more implants or intramedullary cavities in one ormore planes. A further aspect of certain embodiments may allow for theattachment of other instruments that may assist in the physicalalignment, sizing, pin placement, etc. of surgical guides andinstruments (e.g., extra-medullary rod, drop rod, resection guides,drill guides, and the like). Such aspects of embodiments of the presentsubject matter may be used in conjunction with a preoperative assessmentor plan to provide for proper implantation and alignment of prosthesesin a patient.

It may be emphasized that the above-described embodiments, particularlyany “preferred” embodiments, are merely possible examples ofimplementations and merely set forth for a clear understanding of theprinciples of the disclosure. Many variations and modifications may bemade to the above-described embodiments of the disclosure withoutdeparting substantially from the spirit and principles of thedisclosure. All such modifications and variations are intended to beincluded herein within the scope of this disclosure and the presentdisclosure and protected by the following claims.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of the claimed subject matter, butrather as descriptions of features that may be specific to particularembodiments. Certain features that are described in this specificationin the context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesub-combination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

As shown by the various configurations and embodiments illustrated inFIGS. 1-4, an instrument for intraoperative implant templating usingfluoroscopy has been described.

While preferred embodiments of the present subject matter have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the invention is to be definedsolely by the appended claims when accorded a full range of equivalence,many variations and modifications naturally occurring to those of skillin the art from a perusal hereof.

What is claimed is:
 1. An instrument, comprising: a body formed from aradiolucent material; a first set of radio-opaque members disposed inthe radiolucent body, a first member of the first set of radio-opaquemembers elongate from a respective first end to a respective second endalong a first longitudinal axis, and a second member of the first set ofradio-opaque members elongate from a respective first end to arespective second end along a second longitudinal axis, the first andsecond longitudinal axes being substantially parallel, such that thefirst set of radio-opaque members collectively define a first profilethat corresponds to an outline shape of a first portion of an orthopedicimplant over which the instrument is overlaid; and a second set ofradio-opaque members disposed in the radiolucent body, a first member ofthe second set of radio-opaque members elongate from a respective firstend to a respective second end along a third longitudinal axis, and asecond member of the second set of radio-opaque members elongate from arespective first end to a respective second end along a fourthlongitudinal axis, such that the second set of radio-opaque memberscollectively define a second profile that corresponds to an outlineshape of a second portion of the overlaid orthopedic implant, whereinthe third and fourth longitudinal axes intersect to form an acute anglesuch that the first profile differs from the second profile and thesecond profile has a taper in a direction away from the first set ofradio-opaque members.
 2. The instrument of claim 1, further comprising athird set of radio-opaque members disposed in the radiolucent body, thethird set of radio-opaque members collectively defining an alignmentfeature of the instrument.
 3. The instrument of claim 2, wherein thethird set of radio-opaque members includes a peg and a ring.
 4. Theinstrument of claim 3, wherein the ring circumscribes the peg when theinstrument is properly aligned with a first anatomic viewing plane. 5.The instrument of claim 4, wherein the first and second longitudinalaxes define a plane and the ring circumscribes the peg when theinstrument is viewed perpendicular to the plane.
 6. The instrument ofclaim 1, wherein the first and second longitudinal axes are parallel. 7.An apparatus, comprising: a first module, comprising: a firstradiolucent body; a first set of radio-opaque members disposed in thefirst radiolucent body, a first member of the first set of radio-opaquemembers elongate from a respective first end to a respective second endalong a first longitudinal axis, and a second member of the first set ofradio-opaque members elongate from a respective first end to arespective second end along a second longitudinal axis, such that thefirst set of radio-opaque members collectively define a first profilethat corresponds to an outline shape of a first portion of an orthopedicimplant over which the instrument is overlaid in a first plane; and asecond module coupled to the first module, the second module comprising:a second radiolucent body; a second set of radio-opaque members disposedin the second radiolucent body, a first member of the second set ofradio-opaque members elongate from a respective first end to arespective second end along a third longitudinal axis, and a secondmember of the second set of radio-opaque member elongate from arespective first end to a respective second end along a fourthlongitudinal axis, such that the second set of radio-opaque memberscollectively define a second profile that corresponds to an outlineshape of the first portion of the overlaid orthopedic implant in asecond plane, and wherein the first plane and the second plane arenon-parallel.
 8. The apparatus of claim 7, wherein the first plane andthe second plane are orthogonal.
 9. The apparatus of claim 7, whereinthe first module further comprises: a third set of radio-opaque membersdisposed in the first radiolucent body, a first member of the third setof radio-opaque members elongate from a respective first end to arespective second end along a fifth longitudinal axis, and a secondmember of the third set of radio-opaque members elongate from arespective first end to a respective second end along a sixthlongitudinal axis, such that the third set of radio-opaque memberscollectively define a third profile that corresponds to an outline shapeof a second portion of the overlaid orthopedic implant, wherein thesecond portion differs from the first portion.
 10. The apparatus ofclaim 7, wherein the first module further comprises one or more lateralsegments that are configured to couple the first module to the secondmodule.
 11. The apparatus of claim 7, wherein the first module furthercomprises a third set of radio-opaque members disposed in theradiolucent body, the third set of radio-opaque members collectivelydefining an alignment feature of the apparatus.
 12. The apparatus ofclaim 11, wherein the third set of radio-opaque members includes a pegand a ring.
 13. The apparatus of claim 12, wherein the ringcircumscribes the peg when the first module is properly aligned with afirst anatomic viewing plane.
 14. The instrument of claim 13, whereinthe first and second longitudinal axes define a plane and the ringcircumscribes the peg when the first module is viewed perpendicular tothe plane.
 15. The instrument of claim 13, wherein the second modulefurther comprises a fourth set of radio-opaque members including asecond peg and a second ring, and wherein the second ring circumscribesthe second peg when the second module is properly aligned with a secondanatomic viewing plane.
 16. The instrument of claim 7, wherein the firstand second longitudinal axes are parallel.
 17. The instrument of claim7, further comprising one or more rods extending from the first moduleand configured for attaching a resection guide to the first module. 18.An instrument, comprising: a body formed from a radiolucent material; afirst set of radio-opaque members disposed in the radiolucent body, afirst member of the first set of radio-opaque members elongate from arespective first end to a respective second end along a firstlongitudinal axis, and a second member of the first set of radio-opaquemembers elongate from a respective first end to a respective second endalong a second longitudinal axis, the first and second longitudinal axesbeing substantially parallel, such that the first set of radio-opaquemembers collectively define a first profile that corresponds to anoutline shape of a first portion of an orthopedic implant over which theinstrument is overlaid; and a second set of radio-opaque membersdisposed in the radiolucent body, a first member of the second set ofradio-opaque members elongate from a respective first end to arespective second end along a third longitudinal axis, and a secondmember of the second set of radio-opaque members elongate from arespective first end to a respective second end along a fourthlongitudinal axis, such that the second set of radio-opaque memberscollectively define a second profile that corresponds to an outlineshape of a second portion of the overlaid orthopedic implant, whereinthe third and fourth longitudinal axes intersect the first and secondlongitudinal axes at oblique angles.
 19. The instrument of claim 18,further comprising a third set of radio-opaque members disposed in theradiolucent body, the third set of radio-opaque members collectivelydefining an alignment feature of the instrument.
 20. The instrument ofclaim 19, wherein the third set of radio-opaque members includes a pegand a ring, and wherein the ring circumscribes the peg when theinstrument is properly aligned with a first anatomic viewing plane.